The present invention pertains to a sealless connection mechanism for joining strapping materials. In particular, the present invention pertains to a reduced force sealless connection mechanism for use in a strapping machine to create a sealless connection between overlapping strapping materials.
Strapping machines (or “strappers”) are well known in the art. These machines are used for strapping articles, e.g., a load, together with strapping material. Strapping material is offered in a variety of sizes and materials and is generally stored on a roll. Conventional strapping materials include steel and plastic.
Typically, a free end of strapping material is passed around the load until there is an overlap between the free end and the strapping material still connected to the roll. The overlapping portion of strapping material is placed between jaws of a strapping machine and the free end of the strapping material is fixed in place by a gripper portion of the machine. After the strapping material is fixed, the material is tightened or tensioned around the load to a desired tension. This is accomplished by operating a feed wheel, a windlass or similar mechanism to pull back, or tension, the strapping material.
A typical strapper includes sealing heads for sealing the free end of the strapping material onto itself, around the load. Typically, in manual (i.e., hand-operated) strappers, a handle is rotated which applies a force to cause a punch or sealing head to press down against the strap to seal the strap to itself. After the strapping material is sealed, the strapping material still connected to the roll is cut by a cutter, which is a portion of the strapper. This completes one strapping operation. This type of seal, known as a “sealless” connection, is effected by sealing the strap to itself, and differs form those strappers that position a separate piece of material around the tensioned strap.
Typically, such a sealless connection employs one or two longitudinal rows of interlocking joints (or “keys”), each comprising a plurality of shoulders, which are defined by Z-shaped or other slits in the overlapped strapping material segments. The keys are adapted to interlock with each other when the overlapped strapping material segments are released under a tensile load. The overlapped strapping material segments shift longitudinally with respect to each other in a locking direction.
An “anti-reverse” locking means also may be provided for the sealless strap connection, such locking means designed to prevent the overlapped, connected strapping material segments from shifting longitudinally to unlock the interlocking shoulders after creating the sealless connection. One such sealless connection having an “anti-reverse” locking mechanism is disclosed in U.S. Pat. No. 4,825,512 for a “Sealless Strap Connection,” commonly owned with the present application, and incorporated herein by reference.
Regardless of the particular sealless connection configuration, considerable force is required to form the keys in the strapping material and to cut the material. As such, an operator may fatigue from repeatedly applying force while forming the sealless connection, and the strapping machine components may wear, and possibly fail, prematurely.
To help reduce operator fatigue and component wear, and to lessen the force required to operate the strapper, various strapper designs have been developed. One known type of prior strapper uses a cammed arrangement with differently configured cam lobes to sequentially move the sealing heads into engagement with the strap. Although this reduces the amount of force necessary to effect a seal, the mechanical movement (and thus the components required), is complex and results in increased maintenance to the strapper. Since many such strappers are used “in the field” increased maintenance typically results in a tool that has limited usefulness.
Other strapper designs, however, have taken a different approach to lessening the operator force required to create the sealless connection. For example, the prior art includes a strapper having a progressive punch design, such as that disclosed in U.S. Pat. No. 6,554,030 for a “Progressive Punch,” commonly owned with the present application, and incorporated herein by reference. In this device, a progressive punch is used in a strapping machine for positioning and sealing an associated strap material around a load.
The progressive punch is positioned in a strapper jaw assembly that includes a movable punch support and a fixed punch support configured to receive the overlapping strapping material therebetween. The movable and fixed supports each include at least one punch having at least two punching heads. The heights of the punching heads are different from one another so that the punching heads progressively engage the strap, with each punching head initially engaging the strapping material at a different time from the others.
Under such a design, the amount of operator force required to create the seal is reduced by controlling the sequence of the punching heads such that less than all of the punching heads are punching the strapping material at a given time. For example, in a sealless connection design comprising longitudinal rows of three joints (a “three key” joint), as is well known in the prior art, a two-step punching sequence is created when using three punches (two upper punches and single lower punch, each with three punching heads). In the first step, the punching heads simultaneously punch the inner and outer slits of the first and last joints. In the second step, the punching heads simultaneously punch the inner and outer slits of the middle joint.
While this design is an improvement over the prior art and does serve to reduce the force required to create the sealless connection, it does not fully optimize the punching sequence to further minimize the required operator force and to further reduce equipment wear. To with, in the first step, the punching heads simultaneously punch four slits of two joints. It would be advantageous to further reduce the number of simultaneous punches such that no more than two slits of any of the joints are simultaneously punched. The force required to create the sealless connection would then be proportionately reduced.
Accordingly, there is a need for an improved progressive punch design that permits a sufficiently strong sealless connection to be formed with a smaller actuating force than currently required by prior art devices. Desirably, such a progressive punch design includes a plurality of punching heads that are configured in such a manner that no more than two slits of any of the joints are simultaneously punched in the strapping material. Most desirably, such a configuration is achieved through a combination of punching heads having different heights, along with a stepped punch support plate designed to further sequence the engagement of the punches with the strapping material.